Mist spinning process



1968 w. B. HENDERSON ETAL 3,

MIST SPINNING PROCESS Filed 001:. 12, 1964 INVENTORS WILLIAM B;HENDERSON GERD R. BAUR ATTOR United States Patent 3,410,940 MISTSPINNING PROCESS William E. Henderson and Gert! R. Baur, Decatur, Ala.,

assignors to Monsanto Company, St. Louis, Mo., a corporation of DelawareFiled Oct. 12, 1964, Ser. No. 403,190 6 Claims. (Cl. 264-182) ABSTRACTOF THE DISCLOSURE A process, which substantially increases dyereceptivity, tenacity and elongation of acrylic filaments, pro- Thepresent invention relates to the preparation of acrylonitrile filaments.More particularly, this invention relates to an improved dry-jet wetSpinning process for producing acrylonitrile continuous filaments havingvaluable properties as are hereinafter described.

In the production of continuous filaments by the standard dry-jet wetspinning process, a solution of acrylonitrile polymers and copolyme-rsdissolved in a suitable organic solvent is extruded through a spinneretposltioned in close proximity to a coagulating bath which the extrusionsenter to form filaments. Once the extrusions are immersed in the bath,coagulation occurs almost immediately to form filaments that are removedfrom the bath and subjected to various stretch ratios on several pairsof heated rolls operated at different rates of speed to establish draftratios for orienting the molecular structure of the filaments.

The dry-jet wet spinning technique is utilized to facilitate preliminarydrawing and reduce the porosity of the fiber structure whereby the jetstretch is increased to produce a" faster spinning rate. By spacing thespinneret above the coagulating bath, a semi-coagulation zone isestablished wherein the cmbroyic filaments are exposed to the atmospherefor a fraction of a second. During this short interval a membrane-likeskin is formed as an outer coat for the extrusions which strengthensthem and r of desired physical characteristics. The dry-jet wet spinningprocess is limited however, for the reason that the exposure time cannotbe increased because the extrusions tend to coalesce and adhere to eachother if the face of the spinneret is more than one-half inch from thesurface of the bath. Thus, the filaments produced by a standard dry-jetwet spinning process do not meet the necessary requirements for suchproperties as abrasion, dyeing, elongation, and tenacity.

With the foregoing in mindjit is an object of the present invention toprovide an improved dry-jet wet spinning process which acceleratesinitial coagulation of extruded filament-forming material to strengthenthe filaments whereby increased drawing may be imposed prior toimmersion in a coagulating bath to impart desirable physicalcharacteristics to the filaments.

Another object of the present invention is to provide an improvedprocess for increasing the spinning rate of aorylonitrile polymers andcopolymers to produce continuous filaments having improved dyereceptivity, abrasiveness, tenacity, and elongation properties.

A further object of the invention is to provide an im proved spinningprocess wherein the extruded filaments are exposed to an annealingmedium prior to complete coagulation thereof to achieve desirablephysical properties.

Still another object of the present invention is to provide a processfor increasing the amount of jet stretch of filaments to reduce thesurface area thereof before they come into contact with the coagulatingbath and thereby reduce frictional drag between the filaments and theliquid bath.

Other objects and advantages will become apparent from the followingdetailed explanation of the invention.

These and other objects of the invention have been accomplished bypositioning the face of a spinneret or jet from one-half to four andone-half inches from the surface of a coagulating bath comprised of amixture of Water and dimethylacetamide and enclosing the spinneret in achamber having a pair of spray nozzles connected thereto for producing amist or annealing medium which promotes initial coagulation offilament-forming solution of acrylonitrile polymers and copolymers beingextruded thrugh the spinneret into the coagulating bath. The fogatmosphere is comprised of either water or dimethylacetamide or amixture of both atomized by an air supply and is introduced into thechamber through conventional spray nozzles.

In accordance with the present invention, the chamber is filled with thefog atmosphere by a pair of spray nozzles positioned at a level betweenthe coagulating bath and the spinneret and directed toward each other.The emerging filaments are exposed to the semi-coagulating atmosphereimmediately and a skin-like membrane is formed on the outer surfacethereof to strengthen the filaments while the central portions remain ina gel-like state until entering the coagulating bath. The extra strengthimparted to the filaments by he fog amosphere makes possible theimposition of more drawing force on the filaments to achieve a higherjet stretch which results in faster spinning rates and improvesparticular physical characteristics such as dye receptivity, resistanceto abrasion, tenacity, and elongation. Heretofore, these properties havebeen obtained by annealing the filaments in a stretched condition duringa subsequent operation. The faster spinning rate is made possible by thefact that the spinneret can be positioned farther away from thecoagulating bath since the fog accelerate initial coagulation whichstrengthens the filaments and makes them capable of withstanding moredrawing to maintain enough tension on the filaments to preventcoalescence with one another unless the distance exceeds four andone-half inches. Thus, there are two important aspects present which aideach other to accomplish the principal objects of this invention. Forexample, as more initial coagulation occurs the filaments arestrengthened to permit spacing of the spinneret face farther from thecoagulating bath which extends exposure time and causes furthercoagulation.

Another important feature of the present invention which makes fasterspinning speeds possible is the drawing down of the filaments as theyare extruded from the spinneret face before they come into contact withthe liquid coagulating bath where frictional drag normally reduces themaximum speed on unstretched filaments. The attenuating forces imposedon the semicoagulated filaments reduces the porosity of them andpromotes better homogenity. The reduction in diameter of the filamentsis facilitated by the increased jet stretch which is made possible bythis invention. By jet stretch is meant the ratio of the linear rate ofwithdrawal of fibers from the spin bath to the linear rate of extrusionof spinning solution into the spin bath.

The present invention will be more clearly understood by reference tothe drawing which illustrates a side elevation, partly in cross-section,of a dry-jet wet spinning apparatus modified in accordance with therequirements necessary for carrying out the invention.

Referring specifically to the single figure of the drawing, there isshown a spinneret or jet positioned above a suitable liquid coagulatingbath 12 with the face thereof directed toward the bath. The spinneretmay be of any well known type and may be spaced one-half to four andone-half inches from the liquid depending on the results desired. Thespinneret is enclosed in a cylindrical casing 14 having a closureprovided with an opening 18 to receive a rounder arm 20 which suppliesthe spinning solution from a source, not shown, and the other is openbut extends substantially to the liquid bath 12 to form a foggingchamber 22. The spinning solution is extruded through the orifices inthe spinneret 10 and into the liquid coagulating bath 12 to form aribbon of filaments 24. At an elevation intermediate the spinneret andliquid bath, a pair of conventional spray nozzles 26 are positionedinside chamber 22 on each side of the filaments for injecting a mist orfog into the chamber to establish a fog-like atmosphere which functionsas a semi-coagulation zone. The mist or fog is comprised of Water ordimenthylacetamide or a mixture of both and is atomized by pressurizedair, the sources not being shown. The filament ribbon is guided throughthe liquid bath 12 by a pair of bars 28 and withdrawn through a stripperbar 30 before passing over take-up rolls 32.

A clearance is provided around rounder arm 20 at opening 18 and betweencylinder 14 and the liquid bath 12 to permit the exhausting of air fromchamber 22. The chamber remains completely saturated with the atomizedliquid at all times to insure that all surface areas of the filamentsare exposed to the fog atmosphere so that maximum desired results areobtained.

The invention will be further illustrated but is not to be limited bythe following examples. All parts are given by weight unless otherwisespecified.

EXAMPLE I A spinning dope was prepared by dissolving 24 parts of acopolymer comprised of 94% acrylonitrile and 6% vinyl acetate in 76parts of N,N-dimethylacetamide solvent. The dope was heated to 85 C.,filtered, and delivered to the spinning apparatus. The dope was extrudedthrough a spinning jet containing 68 holes 0.010 inch in diameter. Thespinning jet was positioned 3.5 inches above a spin bath comprised ofwater and N,N-dimethylacetamide solvent at 42 C., and was enclosed by amist chamber which extended from above the spinning jet to within A inchof the surface of the spinbath. A mist of N,N-dimethylacetamide solventin air was continuously introduced into the chamber by means of twoopposing spray nozzles. The filaments extruded from the spinning jetpassed through the mist and into the spin bath while undergoing a jetstretch of 6.5x. The coagulated filaments proceeding from the spin bathwere washed with hot water to remove residual solvent, given anadditional stretch of 2.0x to provide molecular orientation, and driedto reduce the moisture content to less than 1.0 percent.

The resulting fiber product was evaluated for physical properties andbasic dyeability. The fiber tenacity was 2.7 grams per denier, andelongation was 49%, as determined by a single filament tests on theInstron tester. The fiber dye acceptance (BDA) was 1.6% dye uptake basedon the weight of fiber.

4. EXAMPLE II The process of Example I was repeated except that the mistchamber was removed and the spinning jet was lowered so that a /2 inchair space existed between the surface of the spin bath and the face ofthe jet. The maxi mum stretch which could be imposed upon the filamentsextruded from the jet and passing into the spin bath was 3.0x. Anadditional stretch of 4.0x was taken during the subsequent washing stepto provide a total filament stretch of 12.0

After the filaments were washed and dried, the tenacity was determinedto be 2.2 grams per denier, and elongation was 24%. The BDA of the fiberwas only 0.6%.

EXAMPLE III The process of Example I was repeated except that a mist ofwater and air was sprayed into the mist chamber. The face of thespinning jet was positioned 2% inches above the surface of the spinbath, and a stretch of 3.1x was imparted to the extruded filamentspassing through the mist chamber and into the spin bath. An additionalstretch of 6.2x was taken during the washing step providing a totalfiber stretch of 19 After the fiber was dried, the tenacity wasdetermined to be 2.9 grams per denier and the elongation 30%.

EXAMPLE IV A spinning solution was prepared by dissolving 16.7 parts ofa first copolymer comprising 94% acrylonitrile and 6% vinyl acetate and2.3 parts of a second copolymer comprising 50% acrylonitrile and 50%methyl vinyl pyridine in 81 parts of N,N-dimethylacetamide solvent. Thesolution was heated to 85 C., filtered, and transferred to the spinningapparatus, where it was extruded through a spinning jet containing 68holes 0.010 inch in diameter. The face of the spinning jet waspositioned 2 inches above the surface of the spin bath, which wascomprised of 45% Water and 55% N,N-dimethylacetamide at 42 C. A verticaltube mist chamber enclosed the spinning jet and extended to within inchof the surface of the spin bath. A mist of N,N-dimethylacetamide solventand air was introduced into the chamber by means of two opposing spraynozzles located approximately midway between the spinning jet and thesurface of the spin bath. A stretch of 3.0x was imparted to the extrudedfilaments while passing through the mist chamber and into the spin bath.An additional stretch of 1.6-X was taken during subsequent washing ofthe coagulated filaments.

After drying, the filamentary tow bundles were texturized according toconventional techniques. The resulting textured yarn was evaluated on anIP-4 tester, and found to have a tenacity of 1.15 grams per denier, andan elongation of 13%. The basic dye acceptance of the yarn was 1.6 gramsof dye per grams of yarn.

EXAMPLE V The process of Example IV was repeated except that a 50/50mixture of N,N-dimethylacetamide solvent and water were sprayed into themist chamber. The texturized yarn product had a tenacity of 1.12 gramsper denier and an elongation of 14%. The basic dye acceptance of theyarn was 1.5 grams of dye per 100 grams of yarn.

EXAMPLE VI The spinning solution of Example IV was extruded through anidentical jet positioned /2 inch above the surface of the spin bath, andnot enclosed by the mist chamber. A first stretch of 1.7 was taken asthe extruded filaments passed from the jet through the air space andinto the spin bath. A second stretch of 2.2 was taken while thefilaments were washed after proceeding from the spin bath.

The dried, filamentary tow bundles were texturized according toconventional techniques. The resulting textured yarn was evaluated onthe IP-4 tester, and found to have a tenacity of 1.14 grams per denierand an elongation of 7.0%. The basic dye acceptance of the yarn was 0.62gram of dye per 100 grams of yarn.

It is obvious by comparing the yarn data of this example with that ofExample IV that the incorporation of the mist chamber device producesyarn with improved physical properties and considerably greateraifiinity for basic dyestuffs.

EXAMPLE VII The process of Example IV was repeated except that the jetenclosed by the mist chamber was lowered so that the jet face was /2inch above the surface of the spin bath, and a water-air mist wassprayed into the chamber. The fiber passing from the jet to the spinbath was stretched 3.0x, and a second stretch of 1.5 X was taken duringthe subsequent washing operation.

The dried filamentary tow bundles were texturized according toconventional procedures, and the resulting yarn evaluated for physicalproperties on the IP-4 tester. The yarn was found to have a tenacity of1.2 grams per denier, and an elongation of 11%. The basic dye acceptanceof the yarn was 1.1 grams of dye per 100 grams of fiber.

It will be understood that various modifications may be made in theembodiment and practice of the invention illustrated and describedherein without departing from the scope thereof except as defined by thefollowing claims.

We claim:

1. A wet spinning process for forming continuous synthetic filamentsfrom a solution comprised of a copolymer of acrylonitrile and a volatilesolvent comprising the steps of:

(a) forming continuous filament lengths by extruding said solution froma spinneret substantially vertically downwardly toward a coagulatingbath and into an enclosed chamber;

(b) coagulating the exterior surfaces of said filamer lengths to formfilaments having a skin comprise essentially of said filament formingmaterial and core gel comprised of said solution by injecting int saidchamber an atomized coagulating liquid, sai atomized liquid contactingand removing said vola tile solvent from the exterior filament surfacest form said skin while said filament lengths pass th distance from saidspinneret to said coagulating bath (0) stretching said filaments whilein contact with sail atomized coagulating liquid to a final length of aleast three times their orginal lengths; and

(d) coagulating said filament core by advancing sai fiber through saidcoagulation bath.

2. The process of claim 1 wherein the atomized fillit is water.

3. The process of claim 1 wherein the atomized fluid idimethylacetamide.

4. The process of claim 1 wherein the atomized fillit is a mixture ofwater and dimethylacetamide.

5. The process of claim 1 wherein said filaments wen stretched at leastsix times their original length.

6. The process of claim 1 wherein said distance be tween said spinneretand said coagulating bath is fron one to four and one-half inches.

References Cited UNITED STATES PATENTS 2,354,744 8/ 1944 Dreyfus 264-1752,688,010 8/1954 Chaney 264-203 )4 2,425,782 8/1947 Bludworth et a1.264-203 2,437,263 3/1948 Manning 264-176 2,542,973 2/1951 Abernethy264-178 2,948,584 8/1960 Euler et al. 264-206 3,097,415 7/1963 Davis264-206 JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner.

